Product category:
Rolling mills and equipment
News Release from: Donix | Subject: Controlled water cooling units software
Edited by the Manufacturingtalk Editorial
Team on 28 July 2006
Complex software controls sheet cooling
system
Automatic control of cooling temperature along 95% of strip length of 4mm stock with the deviation within 10 deg C for the stock thickness 4mm resulted in mill yield increase.
To obtain high mechanical properties of sheet products, hot rolling mills are equipped with controlled water cooling units (CCU) Such units usually include a large number of sections, located above and under the stock in the direction of its movement
This article was originally published on Manufacturingtalk on 11 Apr 2006 at 8.00am (UK)
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Laminar cooling units became especially popular on plate and strip mills.
The main task of the CCU is to ensure the stock cooling at a specified speed down to the specified temperature without its buckling.
Modern requirements to the temperature control accuracy and to its stability along the stock length can be satisfied only through automatic control over the CCU operation.
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RPC Donix offered a conception of automatic control over the sheet products cooling and the basic mathematical software for it which were implemented in 2001 during the upgrade of the laminar strip cooling system on the exit roller table of 1700 mill of OJSC Ispat-Karmet.
At present this system is in permanent use and allows to maintain the specified coiling temperature along 95% of the strip length with the deviation within 10 deg C for the stock thickness 4 mm and +/-15 deg C for the stock thickness over 4mm.
As a result in 2002-2003 if compared with 2000 (period of the cooling system operation before the upgrade) increased of the mill yield according to mechanical properties from 97.1 to 98.9% and significant improvement of the stability of the finished stock properties were observed.
The proposed conception of automatic control over the controlled cooling unit consists in choosing the specified values (tasks) for the cooling section valves control during the stock movement in the prepared table - the so-called 'basic matrix'.
This table contains data on the valves setup for all the combinations of the three process variables - temperature at the entry into the cooling unit, metal speed and deviation of the temperature at the exit from the cooling unit from the specified value - which are possible for the given lot of the rolled stock.
The basic matrix is prepared before the cooling of the stock begins.
So to cool each section along the stock length the controller has just to choose the necessary cell in this table.
To set up the system before the cooling begins the cell which meets the process regulations (initial setting) is chosen in the matrix.
When the cooling begins the cells which meet the actual values from the in-process measurement sensors are chosen in the matrix (correction).
Thus, in case of changes in the temperature at the entry into the CCU or in the metal speed, as well as in case of deviations of the temperature at the exit from the CCU from the specified value the controller program - 'slides' over the matrix, changing from one of its cells to another.
The basic matrix itself is calculated on a separate computer and transferred to the controller before the rolling of the lot begins.
The proposed conception eliminates the necessity of calculating the corrective actions in the controller along the stock movement and ensures the most rapid response of the control system to any disturbances and deviations of the process variables.
In 2005 RPC Donix created a program package for the automated control systems of the CCUs for plate products based on the described conception.
It includes five main software products: Program for the basic matrix calculation includes: visualization program; program for monitoring the stock movement under the CCU; program for the section valves control and program for the design model adaptation.
The package serves as the basic software which can be integrated into the control system of any laminar CCU, existent or being constructed.
To ensure the compatibility with the CCU of any configuration the mathematical model of cooling was improved significantly, if compared with the version implemented on 1700 mill of OJSC Ispat-Karmet.
The programs for the basic matrix calculation and the design model adaptation are realized in Delphi 7 environment.
The visualization program was developed using the Wonderware 'In Touch' program package, included into the general Wonderware FactorySuite? package.
To check and preset the software, as well as to demonstrate its possibilities RPC Donix developed a simulation model of the CCU automated control system.
It simulates the stock cooling process on a certain plate mill on the computer monitor in real-time mode.
The user (mill operator) enters the rolling schedule for a certain period (i e, for the next hour or the next shift) and observes the entire mill operation process on the monitor.
The simulation model works on any IBM-compatible personal computer with the operational system Microsoft Windows XP.
The following data serve as basic input data for the simulation model: layout of the equipment and in-process measurement devices; rated variables of the CCU (permissible water consumption per section etc); inertial characteristics of the cooling unit; actual state of the CCU (numbers of the inoperative sections, dead hydraulic blowoffs); program of the mill usage for the calculated time period with the indication of the sheets quantity, nominal dimensions, steel grade for each lot; process regulations (range) regarding the temperature at the entry into the cooling unit and the stock speed for different products; specified temperature at the exit from the cooling unit for the given lot; specified cooling strategy for the given lot (early, late or uniform); actual temperature at the entry into the cooling unit and the stock speed; cooling water temperature and actual volume of the water in the tanks.
Output data are: numbers of the operating cooling sections; water consumption per section and the sections switching-on and switching-off moments.
The simulation model includes all the five abovementioned software products, as well as an additional program simulating the data which come from adjacent automated control systems, in-process measurement sensors, actuators etc on the real unit.
In the simulation model all these programs work and carry out the data exchange on one computer.
But structurally the simulation model is divided into three big units, corresponding to their physical layout in the real automated control system: calculating unit (operating as the system computer for the basic matrix calculation, the design cooling model adaptation, data archiving, etc); simulation programs unit (operating as the controller monitoring the stock position, controlling the section valves, as well as carrying out the data exchange with the other automated control systems, in-process measurement sensors etc) and visualization unit (operating as the operator's workstation).
If we present the CCU automated control system as a two-level structure, the simulation programs unit builds the lower level realizing the measurement, control, intermediate processing and direct control functions according to the tasks from the upper level or the CCU operator.
The additional simulation program realizes the functions of the adjacent automated control systems of the mill, not included into the CCU automated control system.
The upper level consists of the calculating unit (which ensures the task calculation for the lower level and data storage) and the visualization program (data visualization for the staff).
The developed program package can serve as a base for the creation of an automated system for almost any laminar cooling unit for sheet products.
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